1. Field
Aspects of the present disclosure relate generally to image processing, and more particularly, to a fast vector error diffusion.
2. Background
Halftoning is a reprographic technique that simulates continuous tone imagery through the use of dots, varying either in size, in shape or in spacing. Whereas continuous tone imagery contains an infinite range of colors or greys, the halftone process generally reduces visual reproductions to a binary image that may be printed with only one color of ink. This binary reproduction relies on a basic optical illusion—that these tiny halftone dots are blended into smooth tones by the human eye. Halftoning is also commonly used for printing color pictures. The general idea is the same, by varying the density of the primary printing colors used (e.g., cyan, magenta, yellow and black), a particular shade can be reproduced.
Error diffusion is a type of halftoning in which the quantization residual is distributed to neighboring pixels that have not yet been processed. Its main use is to convert a multi-level image into a binary image, though it has other applications. Unlike many other halftoning methods, error diffusion is classified as an area operation, because what the algorithm does at one location influences what happens at other locations.
In vector error diffusion, each color is mapped to its closest primary and the error between the color and the primary is then propagated to neighbor colors. The larger the number of primaries, the higher the cost to search for the closest primary. For example, if ‘n’ is the total number of primaries, in order to find a closest primary, n distances are computed and n comparisons are performed. If n is large, the computation time and complexity is large, resulting in a very slow process.